Ferrous castings are used in the manufacture of various parts for machines, engines and the like. For example, a crankshaft or steering gear may be a ferrous casting. In the manufacture of a crankshaft, it is often necessary to provide a series of connected non-linear passages through the ferrous casting to carry lubricants. These connected passages are most often conventionally provided into the casting by a gun drilling method. The drilled passages typically require counterboring, tapping, and plugging in order to provide a generally smooth, continuous, winding passage through the casting. This method of providing a continuous passage is relatively expensive and time consuming. In some cases, the drilling operation cannot provide the optimum design from the standpoint of crankshaft functionality, and the crankshaft has to be designed around the limitations of the drilling operation. Thus, there has been a need to provide an improved means for manufacture of such a casting.
Additionally, there exist many applications where ferrous castings possess the requisite mechanical strength properties, but where ferrous castings are presently considered undesirable or unacceptable due to the inherent limitations of other metallurgical properties associated with the castings. For example, crankshaft crankpins inherently provide a rotating mass, and therefore need a counterweight to balance the mass. Large dimension crankpins conventionally give rise to larger counterweights which therefore require a larger crankcase and related engine components. There exists a need to be able to reduce the size of the crankcase and the counterweight independently of the design considerations of the crankpins.
As another example, many applications exist where advantageously part but not all of a ferrous casting is forged and metallurgically bonded to a casting. However, it may be impractical or impossible to provide such a product because of the inability to metallurgically bond forged metal to cast metal. For example, currently automotive and light truck drive line U-joints are welded to the drive shaft tube. Heavy truck torque arms are currently produced by welding a relatively expensive forged eye to the end of a section of heavy walled alloy steel tubing. Both could advantageously be fabricated in part from a casting. However, the U-joint or eye cannot be made in commercial practice by ferrous casting because the casting cannot be easily bonded by welding to the forged tubing.
The art of ferrous castings is well developed. For example, various prior art patents depict processes for the manufacture of castings having complex shapes and forms. Walker in U.S. Pat. No. 1,729,848 discloses a method of manufacture for white iron castings wherein copper plated steel rods are utilized as reinforcements in the casting. Such white iron castings are typically utilized as grates inasmuch as the white iron is not heat treated and is therefore very brittle, yet hard.
Dobovan in U.S. Pat. No. 3,170,452 discloses that a cylinder head of cast iron maybe cast with a wear and corrosion resistant steel metal insert in the shape of a valve seat coated with a suitable brazing alloy. Typically, the insert, which is steel, is coated with a layer of a nickel base brazing alloy. The valve seat is thus cast in place with the gray cast iron.
Vishnevsky, et al. in U.S. Pat. No. 4,008,052 discloses a bimetallic casting wherein a boron containing alloy is provided intermediate the materials being cast. The materials involved are generally known as super alloys.
Spalding in U.S. Pat. No. 4,209,058 discloses yet another die casting operation and, in particular, a casting process whereby a section of steel tubing is die cast in combination with an alloy of magnesium or aluminum.
There has remained, however, a need to provide ferrous castings and methods for making such castings which can be used in a wider variety of applications, as noted above.